Book/Report

FZJ-2019-01660

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Thermisch und durch Elektromigration induzierte Spannung in passivierten Al- und AlSiCu-Leiterbahnen

Beckers, D. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21737

Report No.: Juel-3293

Abstract: Al and Al-alloys are commonly used as interconnect materials in integrated electronic devices. Mechanical stresses in these devices (e.g. caused by the thermal mismatch between the metal and the underlaying Si-substrate and the surrounding passivation) are of special interest because degradation effects such as stress induced voiding or electromigration (EM) are closely related to the stresses in the lines. The strain and stress evolution in thin Al and AISi(1%)Cu(0.5%) films and in passivated lines has been studied by X-ray diffraction during thermal cycling, isothermal stress relaxation and during EM current stressing. Furthermore the extend of voiding and plastic shear deformation of the lines has been determined from the experimental metal strains with the help of finite element calculations and the "eigenstrain" formalism. The evaluation procedure is explained in detail. A comparison to wafer-curvature measurements of the same sampies show good agreement.The main results are: $\textbf{Blanket films}$ The flow stresses in tension (at room temperature) and in compression (at 410°C) vary inversely with the film thickness. In AISiCu-films below 180°C hardening is observed by $\Theta$ - Al$_{2}$Cu-precipitates. The formation and resolution of Al$_{2}$Cu- and Si-precipitates inaddition explain the differences in the unstrained lattice parameters during heating and cooling of the sampies below 250°C. $\textbf{Thermal stresses in passivated lines}$ During thermal cycling the relative volume change by voiding or precipitation is smaller than the experimental error of 3 $\cdot$ 10$^{-3}$. On the other hand almost all samples show shear deformation which depends strongly on the line material and the geometry of the lines. During isothermal relaxation between 2 and 100 h no additional change of plastic shear has been observed but voiding and / or precipitation occured. $\textbf{Current stressing of the lines}$ The EM-force in the lines causes no measurable additional change of the volume averaged strains and stresses up to times of li ne failure. Also the widths of the diffraction peaks showno change compared to the extrapolated progress of the currentless isothermal relaxation. From these observations we have to conclude i) that electromigration damage is not accompanied by an enhanced overall nucleation and growth of voids because this would change the mean stress from the observed tensile regime to compressive. Hence electromigration causes only very few additional voids growing up to a critical size for line failure or the existing void volume is redistributed by theelectromigration-force. ii) that the stress fluctuations $\Delta \sigma_{\infty}$ expected to develop under the influence of the electromigrtaion-force have to be smaller than 260 MPa, which corresponds to the resolution limit of 0.05 degrees in Bragg-peak width.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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